Cardiac arrhythmias occur in as many as 62 percent of anesthetized patients. They interfere with the mechanical performance of the heart and impair myocardial oxygenation in patients with coronary artery disease. It has been generally held that anesthetic-induced changes in pacemaker function are in most cases responsible for these arrhythmias. With the recent application of cardiac electrophysiologic techniques, however, the role of altered conduction in cardiac arrhythmogenesis has become more widely appreciated. Information gained from such studies has been effectively applied by cardiologists in the management of cardiac arrhythmias and conduction disturbances. Comparable data for the effects of anesthetic agents and adjunct drugs on cardiac conduction and arrhythmias do not exist. Utilizing catheter His bundle recordings, premature electrical stimulation and chronically implanted His bundle recording electrodes, we propose to address the question of how anesthetic related changes in conduction are related to arrhythmias. The following studies in dogs will be performed: 1) During halothane or enflurane anesthesia, a discription of conduction changes and supraventricular arrhythmias preceding ventricular sensitization produced by graded continuous infusions of epinephrine; 2) a study of how thiopental modifies the cardiac electrophysiologic events leading to sensitization; and 3) in unanesthetized animals, the determination of how inteavenous and inhalation anesthetic agents modify cardiac conduction. Because arrhythmia mechanisms in dogs and humans are believed similar, we expect our findings to enable anesthesiologists to more effectively manage arrhythmias and conduction disturbances in patients.